Having ended his own presidential run before it began, New York Mayor Michael Bloomberg is now a coveted ally - for any presidential candidate.

Thursday it will be Sen. John McCain at a business roundtable that the Republican presidential hopeful is convening in Brooklyn.

Bloomberg will introduce him with a few kind words, which in some ways is just returning an old favor. In 2001, John McCain was one of the few who endorsed Bloomberg for mayor. But it’s all part of a larger casting call.

Two weeks ago, Barack Obama praised Bloomberg at Cooper Union as the mayor who “shows us what can be achieved when we bring people together.”

CENTRIST OF ATTENTION: Michael Bloomberg would certainly be a key supporter for either Democrat Barack Obama or Republican John McCain.

“He’s like E.F. Hutton now - when Michael Bloomberg talks, people listen,” said Peter Fenn, a veteran Democratic consultant based in Washington D.C.

Many big-city mayors and governors get wooed, but there are differences when it comes to Bloomberg, a Democrat-turned-Republican-turned-independent.

There’s his appeal to voters on both sides of the political spectrum - he may have even run himself under different circumstances, and may merit consideration as a V.P. candidate (though we’re hoping for Condoleezza Rice) - and vast resources.

As a former businessman with deep connections on Wall Street, Bloomberg could also be seen as “a business community stamp of approval,” some beleive.

Aides maintain that Michael Bloomberg remains open to all candidates and will likely back the presidential hopeful who is least afraid to tackle big problems, even if it means telling voters “we can’t afford everything.”